Functionalized Graphene Oxide Enables a High-Performance Bulk Heterojunction Organic Solar Cell with a Thick Active Layer

Novel functionalized graphene oxide pi-pi stacking with conjugated polymers (P-GO) is fabricated via a simple ethanol-mediated mixing method, leading to better dispersion in organic nonpolar solvents and bypassing the inherent restrictions of hydrophilicity and oleophobicity. We analyze the mechanism of the incorporation of P-GO into inverted organic solar cells (OSCs) based on a poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b' dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl) carbonyl] thieno [3,4-b]thiophenediyl]] (PTB7):[6,6]-phenyl C-71 butyric acid methyl ester (PC71BM) system to investigate the possibility of high-performance thick-film OSC fabrication. It is verified that the incorporation of P-GO into the PTB7:PC71BM blend films leads to a decreased pi-pi stacking distance, enlarged coherence length for polymer, and optimized phase separation, resulting in more effective charge dissociation, reduced bimolecular recombination, and more balanced charge transport. The OSCs with 1% P-GO incorporation demonstrate a thickness-insensitive fill factor (57.8%) and power conversion efficiency (PCE) (7.31%) even with 250 nm thick photoactive layers, leading to a dramatic PCE enhancement of 34% compared with the control devices with the same thickness.